Nick - I don't know for sure, but when I installed a changer in my '98 E320,
I used a changer from a '98 SLK (had to use a different mounting bracket) -
at that time, I was told that most changers would fit except for those from
the M-class. In my case, I believe that the changer was an Alpine and
aftermarket units would also fit.
You will almost certainly be pre-wired for a CD changer - In may case it was
hidden behind the trunk lining in the trunk, but behind the back seat - all
I had to do was plug it in.
The 99s may be different from the '98's, but I would think any MB changer of
the same model year would work (except perhaps for those from an M class.)
Any MB dealer should be able to confirm this.
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